Thermally excited near-field source

ABSTRACT

A high resolution material observation system includes an object having at least one spatial dimension sufficient to support production of near-field infrared emissions, a holder adapted to receive a sample to be observed, the holder further adapted to position the sample in the near-field infrared emissions, and a thermal excitation unit, adapted to be thermally coupled to at least one of the object and the sample. The thermal excitation unit is further adapted to causing black body radiation in either the object or the sample within the infrared spectrum.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority from U.S. patentapplication Ser. No. 11/519,393 filed on Sep. 12, 2006, now U.S. Pat.No. 8,160,223 the entire disclosure of which is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to near-field light sources,and, in particular, to near-field light sources generated bynanoheaters.

BACKGROUND OF THE INVENTION

Many applications depend on the ability to read or sense information atvery high resolution. For example, in a storage system, such as a CD(compact disc) reader, a focused laser beam is used to read informationpatterns on a disc. However, since such conventional optics is based onrefraction and focusing of electromagnetic radiation, it comes with afundamental constraint in spatial resolution. Specifically, thepropagation of electromagnetic radiation over distances larger than theoptical wavelength (λ) acts as a filter of finite spatial bandwidth,which results in the familiar diffraction limited resolution of ≈λ/2.For example, for λ=1 μm, the maximum possible spatial resolution is ≈0.5μm, which is far from adequate in many now-known and futureapplications.

As a solution to this resolution problem, near-field techniques haverecently been introduced by utilizing non-propagating “near-fields” (D.W. Pohl et al., Appl. Phys. Lett. 44, 651 (1984); A. Lewis et al.,Ultramicroscopy 13, 227 (1984)). Due to the lack of propagation, suchfields do not obey the diffraction limit (M. A. Paesler, P. J. Moyer,Near-field Optics (John Wiley & Sons, New York, 1996)). Generallyspeaking, in order to generate such near-fields, (i) an incident drivingfield with the wavelength λ_(i) and (ii) an object (e.g., asubwavelength aperture, a sharp object tip, or a sharp edge) with muchhigher (spatial) wavelengths λ_(o) (λ_(o)<<λ_(i)) is needed. Such anarrangement will be referred to herein as a “near-field source,” whichcan “focus” or “concentrate” electromagnetic radiation far below thediffraction limit. This near-field source can then be used to exciteanother object (typically a sample), which will be referred to herein asa “near-field receiver.” The response of the near-field receiver, due tothe excitation of the near-field source, results in the generation ofpropagating waves (e.g., due to scattering, absorption, extinction,fluorescence, chemilumninescence etc.), which can then be monitored inthe far-field by some conventional detector setup.

FIGS. 1-3, in conjunction with the following explanation, give examplesof how such near-field sources have been realized. Referring first toFIG. 1, most near-field sources utilize a subwavelength aperture 100,which is placed in a propagating wave 102. In most cases, thepropagating wave 102 is a focused laser beam (e.g., as is shown in U.S.Pat. No. 4,604,520). In this example, a small fraction of the incomingfield 102 is converted into a non-propagating near-field 104, which“leaks” out of the aperture 100 and can be used to excite a sample/workpiece (not shown).

In an alternative approach, as shown in FIG. 2, which can offersubstantially higher resolution and stronger near-fields, a sharp objecttip 200 is driven externally by an electromagnetic laser field 202 inorder to generate a highly localized near-field source 204 (e.g., U.S.Pat. No. 4,947,034). In some cases, antenna effects are exploited tofurther enhance the strength of the near-field (e.g., U.S. Pat. No.6,771,445; see also “Strength of the electric field in aperturelessnear-field microscopy” Y. C. Martin, H. F. Hamann, H. K. Wickramasinghe,J. Appl. Phys. 89, 5774 (2001))

As a third example, FIG. 3 shows a driving field 302 that is reflectedvia internal reflection at a surface 304 of a prism 300 (e.g., as isshown in U.S. Pat. No. 5,018,865). On the outside of the prism 300, dueto the abrupt change at the prism-air interface 304, a“one-dimensional”electromagnetic near-field 306 is generated, whichdecays exponentially away from the surface 304, but which is stilldiffraction limited in the lateral dimensions.

Unfortunately, the arrangements of FIGS. 1-3 in addition to generating alocalized non-propagating near-field, also scatter some of the drivingfield into the far-field. As a result, some fraction of the drivingfield directly hits the detector. Such signals are referred to as“background” and are shown as elements 106, 206, and 308 in FIGS. 1-3,respectively.

The usefulness or quality of a near-field source is largely determinedby the ratio of near-field versus far-field (background) signalstrengths. All traditionally-used near-field sources (FIGS. 1-3) forreading information have in common that the driving field is generatedby a laser or other light source. As a result, the various methods forgenerating near-fields are accompanied by several difficulties andchallenges. Some of the near-field sources show low near-field strengths(FIG. 1) and low confinement (FIGS. 2 and 3). Others, such as that shownin FIG. 2, although providing strong near-fields and very highconfinement, can generate fairly large propagating background signals atthe same wavelength as the near field energy due to the driving field202, which can somewhat obscure the response of the near-field receiver.In addition, the strength of near-field of these configurations is verysensitive to the polarization, the wavelengths, and the focus of thedriving field, which further complicates the control of such near-fieldsources.

Therefore a need exists to overcome the problems with the prior art asdiscussed above.

SUMMARY OF THE INVENTION

The present invention provides a high resolution material observationsystem that includes an object having at least one spatial dimensionsufficient to support production of near-field infrared emissions, aholder adapted to receive a sample to be observed, the holder furtheradapted to position the sample in the near-field infrared emissions, anda thermal excitation unit, adapted to be thermally coupled to at leastone of the object and the sample, the thermal excitation unit beingfurther adapted to causing black body radiation in the at least one ofthe object and the sample within the infrared spectrum.

In accordance with another feature, the invention also includes acontroller for positioning the object relative to the sample.

In accordance with a further feature, the invention includes a detectoroperable to measure a far-field response produced by an interaction ofthe object and the sample in the near-field infrared emission.

In accordance with yet another feature, the present invention includes adetector operable to measure a near-field response produced by aninteraction of the object and the sample in the near-field infraredemission.

In accordance with other features of the present invention, the detectoris a near-field microscope which measures the near-field infraredemission.

In accordance with a further feature of the present invention, theobject and the thermal excitation unit comprise a resistive heater witha first dimension substantially equal to one half of a wavelength of thenear-field infrared emission and a second dimension much less than thewavelength of the near-field infrared emission, where the firstdimension is perpendicular to the second dimension.

In accordance with one added feature of the present invention, theresistive heater includes a first plate and a second plate, where theplates each have an edge that is perpendicular to the first dimensionand larger than the second dimension.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separate viewsand which together with the detailed description below are incorporatedin and form part of the specification, serve to further illustratevarious embodiments and to explain various principles and advantages allin accordance with the present invention.

FIGS. 1-3 illustrate prior art near-field sources.

FIG. 4 illustrates a near-field source and sample arrangement inaccordance with an embodiment of the present invention.

FIG. 5 is a block diagram of a near-field object, sample, and detectionarrangement, where the object is used as the near-field source inaccordance with an embodiment of the present invention.

FIG. 6 is a block diagram of a near-field object, sample, and detectionarrangement, where the sample is used as the near-field source inaccordance with an embodiment of the present invention.

FIG. 7 is a block diagram of a near-field object, sample, and detectionarrangement, where the object and the sample are both used is used asnear-field source and as a near-field receiver in accordance with anembodiment of the present invention.

FIGS. 8A-8G illustrate various embodiments of objects suitable for useas a near field source or receiver in accordance with embodiments of thepresent invention.

FIGS. 9A-9I illustrate various near-field sources using thermalexcitation or cooling in accordance with an embodiments of the presentinvention.

FIG. 10 is a side-elevational view of a nanoheater (infrared lightsource) in accordance with an embodiment of the present invention.

FIG. 11 is a side view of the nanoheater of FIG. 10 includingelectromagnetic radiation patterns, in accordance with an embodiment ofthe present invention.

FIG. 12 is a diagrammatic view of a near-field microscope which utilizesnear-field IR radiation from a tip of an object to realize spectroscopyand microscopy at very high resolution in accordance with an embodimentof the present invention.

FIG. 13 is a diagrammatic view of a heated object used as a near-fieldsource to read an information pattern on a rotating disc, in accordancewith an embodiment of the present invention.

FIG. 14 is a diagrammatic view of an imaging system using an object as anear-field IR receiver and a sample as a near-field IR source, inaccordance with an embodiment of the present invention.

FIG. 15 illustrates an IR power flow vs. distance from a near-field IRsource, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

While the specification concludes with claims defining the features ofthe invention that are regarded as novel, it is believed that theinvention will be better understood from a consideration of thefollowing description in conjunction with the drawing figures, in whichlike reference numerals are carried forward.

Described now is an exemplary apparatus and method for driving andutilizing a near-field source for reading information at asub-wavelength resolution. The present invention circumvents severalproblems associated with the prior-art methods of laser excitation, issimpler and significantly less expensive. Specifically, embodiments ofthe present invention excite a near field electromagnetic sourcethermally, which is realized in an embodiment by a temperaturedifference between source, receiver, and detector. The near field sourcehas at least one dimension that is much smaller than the wavelength ofthe emitted light. The result is a strong and almost background freenear-field source, which can then be used for applications such asreading and/or sensing information at a very high resolution that is farbelow the diffraction limit.

Referring now to FIG. 4, an embodiment of the present invention isshown. A sphere 400 represents a thermally excited near-field source,which has a temperature that is higher than the temperature of a sample402. It should be noted that in this particular example, any near-fieldsgenerated in the sample 402 itself are ignored. Thus, the sample 402 isconsidered a “pure” near-field receiver. In general, the averagedsquared voltage of a resistor due to thermal excitation is given by theNyquist theorem <V²>=√{square root over (4kTRΔf)}, where k is theBoltzmann constant, T the temperature, R the resistance, and Δf thebandwidth. For the embodiment of FIG. 4, the resistance of the sphere400 with a radius “a” is approximated by R≈σ/a, where σ is theresistivity of the sphere 400. The bandwidth Δf depends on thetemperature of the sphere with Δf=kT/h, where h is Planck's constant.The averaged square amplitude of the resulting internal driving field ofthe sphere can then be approximated by <E_(o) ²>≈k²T²σ/ha³. As anexample, a T=1000 K hot sphere with a=10 nm and a resistivity of σ=10⁻⁵Ωm corresponds roughly to an optical driving field of 10 mW focused to aspot radius of 0.5 μm (@ 633 nm).

As in the case of a laser excitation, the thermally generated drivingfield (<E_(o) ²>) will result into a strong localized near-field 404.This near-field source can then be used to excite a near-field receiver402 (e.g., sample or work piece). The sample 402 generates—due to theexcitation by the near-field source—propagating waves 406. Thepropagating waves 406 (i.e., signal) can then be detected in thefar-field. As a comparison, if the sphere 400 were instead heated by theprior-art method of laser excitation, the sphere 400 would radiateadditional propagating far-field waves 408 as a background. However, incontrast to the laser excitation of conventional systems, one embodimentthe present invention provides the advantage that thermal excitation canbe applied locally to the near-field source, which significantly helpsto reduce background signals. In fact, the only background signal causedby the thermal excitation is the resulting black body far-fieldradiation, which can be many orders (>4) of magnitude weaker than thethermal near-field components. Such a high ratio between near-field andfar-field (background) strength can not be obtained easily by any of theprior art arrangements shown in FIGS. 1-3. In addition, experiments showthat the resolution of these thermally excited near-field sources isvery high—in fact much higher than what can be obtained by the exemplaryprior-art arrangements shown in FIGS. 1 and 3.

In summary, the present invention exploits temperature differencesbetween a source and a receiver, which results in an almost backgroundfree, easy to use, and low-cost near-field apparatus for readinginformation at very high resolution. In some embodiments of the presentinvention, the thermally-generated driving field consists of severalfrequencies (i.e., from DC to kT/h) and, therefore, the resultingnear-field component may involve several frequency components as well.In these embodiments, surface waves and/or shape resonances in thenear-field source object can be exploited to select a few frequencies,which can result in a near-field source that emits near field energywith defined wavelength bands or that are monochromatic. In addition,the temperature of the near-field source may be used to adjust or tunethe frequencies of the thermally generated near-field source ifnecessary or desired.

FIG. 5 is a block diagram illustrating one embodiment of the presentinvention. The invention, which is used to detect information atsubwavelength resolution, includes an object 502, such as an object,with a temperature T₅₀₂, a sample or work piece 504 with a temperatureT₅₀₄, a controller 506, which positions the source 502 relative to thesample 504, means 508 to excite or drive the source 502 and/or sample504 thermally (i.e., means to generate a temperature difference betweenobject/sample/detector) and also means 510 to detect the near-fieldinteraction response including a detector with a temperature T₅₁₀.

In this embodiment, the object 502 acts as the near-field source and thesample/work piece 504 acts as the near-field receiver. In this case, thetemperature of the object 502 is higher than the temperature of thesample (T₅₀₂>T₅₀₄). In other embodiments, as shown in FIG. 6, forinstance, the sample/work piece 504 is the near-field source and theobject 502 is the near-field receiver. In this alternative embodiment,the sample 504 temperature is higher than the object 502 temperature(T₅₀₄>T₅₀₂). In yet another embodiment of the present invention, asshown in FIG. 7, the sample/work piece 504 as well as the object 502 actas a near-field source and receiver at the same time. In this case, boththe object 502 and sample 504 are roughly the same temperature and thedetector 510 is at lower temperature than object 502 and/or sample 504(T₅₀₂≈T₅₀₄; T₅₀₂<T₅₁₀). In the following sections, the differentcomponents of the invention are discussed more in detail.

The Object

Except as discussed below, the object 502 is not restricted to anyparticular shape or dimensions and can be made of any material. However,the following considerations can be used as a guideline in selecting anobject 502.

-   -   (i) Generally, if the object is used as a near-field source, the        strength of the thermally excited near-field should be enhanced.    -   (ii) If the object is used as a near-field source, in some        applications, it is desirable to select certain frequencies for        the near-field spectrum    -   (iii) If the object is used as a near-field receiver, it is        preferred to optimize the efficiency, with which the object can        convert the near-field energy into propagating waves.    -   (iv) Regardless of whether the object is used as a near-field        receiver or source, the dimensions of the object should be        chosen to match the target resolution of the apparatus.    -   (v) For some applications, it may be more advantageous to        integrate a local heater or cooler and/or sensor, such as        thermocouple, into the object, which helps to control the tip        end temperature more accurately and can be used as an additional        readout signal. In such situations, the design is more        constrained and typically largely determined by the        heater/cooler/sensor requirements. Such objects are discussed in        detail below.

More specifically, and with reference to FIGS. 8A-G, in terms ofgeometry, very often elongated shapes with high major axis/minor axisratios are preferred. This includes ellipsoids/spheroids (FIG. 8A),semi-ellipsoids/spheroids attached to a plate (FIG. 8B), cylinders/rods(FIG. 8C), cylinders/rods with rounded or pointed ends (FIG. 8D),pointed or rounded triangular/pyramidal shapes (FIG. 8E), rectangulargeometries (FIG. 8F) or any kind of combinations of more than one of theobject shapes (FIG. 8G). These geometries can enhance the strength ofthe near-field due to antenna-like behavior. Furthermore, the pointedobject acts as an additional concentrator of the emitted near-fieldenergy, which boosts the sensitivity as well as the resolution of theapparatus. As an additional advantage, theses structures can also showlarge efficiencies to convert near-fields into propagating fields.Finally, some elongated objects can be designed to enhance and tuneresonance in the object. These effects can then be exploited to engineerobjects with an almost monochromatic near-field spectrum ranging fromdeep IR to near IR.

With regard to the dimensions, generally the object 502 or the objectend (b) is significantly smaller than the sample 504, because the object502 determines the resolution. In most cases, the object width (b) issignificantly smaller than the wavelengths involved. For example, atT=1000 K the peak wavelength in the black body radiation is 2.3 μm(Wien's displacement law), whereas the (nominal) radius or the size ofobject (b) is typically in the 10 nm range. If the near-field source 502generates a narrow window of wavelengths (λ) (e.g., by resonance in thenear-field source), then it is advantageous to adjust the dimensions ofthe object to these wavelengths. For example, if the near-field objectsource contains mostly wavelengths of ≈λ, one can adjust length (a) ofthe object to a≈λ/2 and select the width (b) (and c in FIG. 8F) to be assmall as possible in order to most efficiently exploit antenna resonanceeffects. Finally, if several objects are involved to generate a strongerthermally generated near-fields (see FIG. 8G), the preferred distance(d) between them is as small as possible (d<b).

In terms of the materials, there may be very different preferencesdepending on whether the object 502 is used as a receiver or near-fieldsource (see FIG. 5 vs. FIG. 6). In the embodiment where the object isthe near-field source (FIG. 5), a highly resistive, but still conductingmaterial (e.g., carbon, thin metal films, Si) may be chosen, because,according to the Nyquist theorem, the higher resistance causes astronger driving field (<E_(o) ²>) for a given temperature. In addition,if the near-field source 502 is heated to a high temperature, a highermelting temperature material is preferred. Furthermore, a strongpositive temperature dependence of the resistivity may be advantageous(i.e., the resistivity increases with increasing temperature), whichenhances the strength of the driving field at elevated temperatures.Finally, if the near-field source 502 should provide certain frequencies(e.g, for localized IR microscopy and spectroscopy), materials thatallow the appropriate resonance are preferred. For example, all theIII-V and II-VI semiconductors show a sharp surface wave resonance inthe mid infrared band (as described by A. V. Shechegrov et al., Phys.Rev. Lett. 85, 1548 (2000)), which can be used to enhance certainfrequencies. In case the object is utilized as a near-field receiver,materials are preferred which show large scattering efficiencies (e.g.Au, Al) in the appropriate wavelength range. In some cases, materialswith a resonance may be exploited to enhance the scattering efficiency.

Sample/Work Piece

The sample or work piece 504 is not limited to any particular materialor any dimension or shape. The sample 504 may include informationpatterns consisting of topographic (e.g. little protrusions), optical(e.g. little islands of a differing materials with differing opticalindices) or even magnetic features. In terms of the sample shape, it isadvantageous that the sample is overall flat so that it can be readfaster. In general, for an optimum reading, one may want to match thesample features to the object dimensions. If the object is used as anear-field receiver and the sample as the near-field source, it may bepreferred to have little protrusions on the sample as the informationpattern. This will enhance the strength of the near-field and thereforethe sensitivity/speed of the apparatus. If the sample 504 is heated,then, naturally, a higher melting temperature for the sample isrequired.

Controller

As shown in FIGS. 5-7, the present invention includes a controller 506to position one or both of the object 502 and the sample 504 withrespect to each other. In some embodiments, the controller 506 includesa sensor, which monitors the position of the object relative to thesample. This sensor is often used to produce an error signal for afeedback loop, which controls a positioning device (e.g. a piezoelectric actuator) to match a desired position. More specifically, theobject 502 could be a replacement for an atomic force microscope (AFM)or scanning tunneling microscope (STM) tip and the positioning isrealized with conventional AFM or S™ feedback techniques. In otherarrangements, and in analogy to magnetic storage technology, thiscontroller 506 includes an air bearing mechanism in combination withadditional sensors and electronics for lateral positioning of the object502.

Means for Thermal Excitation

The near-field source (i.e., object 502 in FIG. 5, sample 504 in FIG. 6,or object 502 and sample 504 in FIG. 7) is thermally excited in oneembodiment of the present invention. Generally, this is realized by atemperature difference between the source and receiver and/or detector.For example, in FIG. 5, the object 502 can be heated relative to thesample 504 and/or the sample 504 can be cooled relative to the object502. In FIG. 6, the object 502 can be cooled relative to the sample 504and/or the sample 504 can be heated relative to the object 502. In FIG.7, object 502 and sample 504 are roughly at the same temperature and thedetector 510 is at a lower temperature. Typically, that is accomplishedby cooling the detector 510 and/or heating sample 504 and object 502.Various types of heating and cooling schemes can be applied. Heating(relative to the detector temperature) is preferably applied to thesmallest possible area, which helps to reduce background far-fieldradiation. On the other hand, in case of cooling (relative to thedetector temperature) a larger cooled area may be advantageous becauseit will minimize background contributions due to the black bodyradiation.

More specifically, FIGS. 9A-I show possible examples of configurationsthat can be used for heating and/or cooling the sample 504 or object502. In FIG. 9A, a laser 902 is focused via a lens 904 on a plate 906 towhich the object 502 is attached. The absorbed laser light will heat theplate 906 and therefore the attached object 502, which then can act as anear-field source. The plate 906 can be the cantilever of an atomicforce microscope object. In these embodiments, the laser 902 is able tobe selected to have a wavelength remote from the near-field radiationbeing generated by the heated source.

In FIG. 9B the plate 906 is heated with current I supplied to a resistor908 which is attached to the plate 906.

FIG. 9C shows a cooling scheme, where the cooled junction 910 of aPeltier element is attached to the plate 912. The Peltier elementincludes two different metal stripes 914, 916 connected to a currentsource I. The hot junction 918 of the Peltier element is further awayfrom the object and thus does not influence the object temperaturesignificantly.

FIG. 9D illustrates how an object 920 can be heated very locally bymounting a resistor 922 to its end, which is connected via transmissionlines 924 to a current source I.

FIG. 9E illustrates a cooled junction 926 of a Peltier element directlymounted to the end of the object 928. In comparison to FIG. 9D, theheater of FIG. 9E is made from two different metallic strips 930, 932through which current I is passed. The hot junction 934 is arranged tobe further away from the object and therefore does not influence thecooling.

In FIGS. 9F and 9G, the sample 936 is heated via a laser beam 940, whichis focused with a lens 938 onto the work piece 936. FIG. 9F illustratesa geometry where the laser beam 940 is incident from the same side asthe object 942, while in FIG. 9G, the laser is brought in from theopposite side. FIG. 9H illustrates a resistor 944 attached to the sample946 which is heated by supplying a current I. The laser beam 940 is usedin these embodiments to thermally excite near field sources and isselected to have a wavelength remote from the wavelength of thenear-field energy of interest being generated by the sources.

Finally, FIG. 9I illustrates the sample 936 cooled with cold junction948 of a two metal strip 950, 952 Peltier element, through which currentI is passed. Again in analogy with previous cases the corresponding hotjunction 954 is arranged far away from the object in order to achieveeffective cooling.

Nanoheater

FIG. 10 shows an infrared (IR) light source 1000, referred to herein asa “nanoheater”, according to an embodiment of the present invention,which can be used for generating IR near-field radiation. The nanoheater1000 includes two electrodes 1002 and 1004 connected by a thin strip ofconductive material 1006 forming a nanoheater. 1006 can be heated usingJoule heating by applying a current I. The heating creates chargefluctuations, which are illustrated in FIG. 10. The geometric dimensionsof the nanoheater 1000 are such that the length of the strip 1006, andthus the separation of the plates 1002 and 1004, is about half of awavelength of black body (BB) radiation, i.e. ˜λ_(BB)/2. BB radiation isthe radiation emitted from a sample. The width d of the strip 1006 ismuch less than a wave length of the BB radiation, i.e. d<<λ_(BB). Thesmall width of the strip 1006 causes the strip 1006 of the nanoheater toradiate concentrated near-field energy, and the length of the strip 1006causes this near-field energy to have a wavelength in the vicinity ofλ_(BB).

FIG. 11 shows a side view of the nanoheater 1000 resting on a substratematerial 1101. A current I flows from one electrode 1002 to the other1004, thereby creating a coherent infra-red far-field radiation 1104 anda strongly enhanced infra-red near-field radiation 1102. The FIG. 11illustrates how the near-field of the nanoheater can be used to detectsome molecules in the close vicinity of the nanoheater. It alsoillustrates how the coherent, antenna-like far-field emission of thenanoheater.

The nanoheater 1000 is a very small and strong coherent IR light source.It exploits geometrical, plasmonic, and antenna-like resonances toconfine thermally-activated charge fluctuations. Through use of thenanoheater 1000, the IR emissions can now be characterized as a functionof heater material, geometry, temperature, and others (i.e., degree ofcoherence, spectrum, far-field, and near-field intensity). A nanoheater1000, in accordance with one embodiment of the present invention, has anenergy range of 0.15-0.3 eV (4-9 μm). The spatial resolution ranges fromdiffraction limits in the far-field to about 0.1 microns in thenear-field. In addition, the intensity is greater than 100 timesconventional in the far-field and over 1000 times conventional in thenear-field (similar to IR synchrotron).

As was discussed with reference to FIG. 4, radiation 406 is generatedthrough the excitation of the near-field receiver 402 by the near-fieldsource 400 and is detected in the far-field. This radiation can be theresult of any response of the sample due to the object includingscattering, absorption, extinction, fluorescence and chemiluminescence.A detection arrangement, in accordance with one embodiment of thepresent invention typically includes: (i) an appropriate optical system(e.g., lenses, minors, gratings, beamsplitters etc.), which guides theradiation and (ii) a suitable detector, which turns the radiative powerinto a current or voltage. In principle, the detection can be realizedin various ways, typically classified in two groups: a transmission (seefor example FIGS. 12 and 13) or a reflection (see FIG. 14) geometry. Ingeneral, a variety of optical components can be used. However, since thewavelength range of the near-field source extends typically from nearinfrared (1 μm) to deep infrared (10 μm), infrared suitable opticalcomponents are preferred including reflective (e.g., parabolic, ellipticobjectives made out of Au or Al, for instance) and transmissive optics(e.g., lenses made out of BaF₂, CaF₂, and others). Several types ofdetectors can be used including IR-sensitive photoconductive (e.g.,PbSe, HgCdTe), or photovoltaic (e.g., InSb) detectors as well as “heat”detectors such as pyroelectric devices or thermocouples. It may bepreferred to cool the detectors to reduce noise and enhance thesensitivity. For spectroscopic applications the detection system mayinclude a suitable spectrometer (grating or prism), which can dispersethe different wavelengths scattered by the object and/or sample. Ingeneral, detection systems used by various IR imaging and/or observationsystems are able to be effectively incorporated into one embodiment ofthe present invention.

FIGS. 12-14 illustrate three embodiments of the present invention. FIG.12 shows a near-field microscope which exploits the near-field IRradiation generated by an object 1204 to realize spectroscopy andmicroscopy at very high resolution. Specifically, the cantilever 1202 isa source holder that holds an object 1204 and that is heated by aresistor 1206, which is connected via transmission lines 1208 to acurrent supply I. The object 1204 attached to the heated cantilever 1202is held by a feedback control 1242 over the sample 1212 surface.Specifically, the cantilever 1202 is vibrated with a piezoelectricactuator 1214, typically at one of its resonances. The vibration ismonitored by a deflection system (1216 and 1218). A laser 1220 (e.g.,laser diode) is focused on the back of the cantilever 1202 and itsreflection is picked up by a position sensitive detector 1218 (e.g.,split Si-photodiode) to monitor the motion of the cantilever 1202 andtherefore the source object 1204. The vibration amplitude is measuredwith an electronic system 1216 (e.g., lock in amplifier). Its magnitude(error signal 1222) is compared to a set point, which controls thez-position 1224 of the sample 1212 with respect to the object by anactuator 1224. Actuator 1224 of this embodiment is a holder that isadapted to receive the sample 1212 and position the sample 1212 in thenear-field infrared emissions produced due to the geometry of the object1204.

It is noted that there are other alternatives for the above describedAFM-feedback control including the measurement of the frequency of thevibration (FM-technique). In the example of FIG. 12, the feedback isrealized digitally using a computer 1226, which also controls thescanning (x,y position 1228). The near-field of the heated object isused to excite the sample 1212 (e.g., molecules, etc. being observed),which is arranged on a substrate 1230 with high transmissivity in the IRband (e.g., Si). The radiative response of the sample due to theexcitation by the near-field source is picked by a high numericalaperture reflecting objective 1232. The signal is imaged onto a pinholeor slit 1234, then reflected by a grating 1236 of an IR-spectrometer1240, refocused onto another pinhole or slit 1238 and finally measuredby detector 1244.

The grating 1236 position can be tuned by a computer, which allows forrealization of wavelength resolved microscopy at high resolution. Incases, where the signal strength is fairly low, it may be preferred tomeasure the signal in AC by a lockin amplifier at the vibrationamplitude of the cantilever. In order to measure the total signal onecould remove the grating 1236 and/or the slits/pinholes 1234, 1238.

FIG. 13 shows another embodiment, where a heated object is used as anear-field source 1302 to read an information pattern on a rotating disc1304. In this example, the object 1302 includes a small resistorsandwiched by two larger transmission lines 1306, which are connected toa current supply 1308. The heated object 1302 is integrated into aslider as a reading head 1310. This reading head 1310 flies via anair-bearing surface over the disc at a very close distance. As anexample, the disc substrate 1312 can be a high transmissive materialsuch as CaF₂ and Si, while the bits 1314 are made out of a highreflecting and/or absorbing material (e.g., Au). The resulting radiationis picked up with a lens 1316 and imaged onto a detector 1318. In orderto achieve reading speeds of >100 MHz a shot-noise limited detection ofat least 1 μA is required. The lateral position of the reading head 1310with respect to the disc 1304 is adjusted by a controller 1320, whichalso controls the motor 1322 and the spindle 1324 for the rotation ofthe disc 1304.

As a third embodiment, FIG. 14 shows a different application, where thetemperature distribution of the sample can be measured at highresolution. In contrast to FIGS. 12 and 13, the object is the near-fieldreceiver 1404 and the sample is the near-field source 1402. As anexample, a tiny heated transmission line 1406 within a semiconductorchip is chosen as the sample. If the transmission line dissipates powerand consequently heats the chip, the heat generates a near-field in thevery close proximity to the surface of the sample (in analogy to FIG.3). The strength of this near-field represents the local temperature.Because this near-field is very short-ranged in the z-direction, itprovides a mean for high spatial resolution imaging. As the AFM-object1402 is scanned with an actuator 1408 controlled by the computer 1410laterally (x,y position 1412) it “releases” and radiates the frustratednear-field radiation within the chip and maps out the temperature/heatdistribution at the sample at high resolution. This radiation is pickedup by a reflecting objective 1414 and imaged with a lens (e.g. Si, 1416)onto a suitable detector 1418 in a reflection geometry. The output ofthe detector is connected via a detector input 1420 to the computer1410, which allows construction of a temperature image as a function ofobject 1402/sample 1414 geometry.

In FIG. 12, a deflection system was used to monitor the cantilever 1202vibration. However in this embodiment we use a heterodyne interferometersystem 1422 and excite the cantilever 1424 with a small piezoelectricactuator at or near one of its resonances 1226. This heterodyneinterferometer system may include various optical components/detectorsand a laser 1228 as well as a lockin amplifier, which measures theamplitude of the vibration as well as other electronic components. Theamplitude is used in a computer 1410 controlled feedback loop as theerror voltage 1430 to control the z-position 1432 of the actuator 1408.The heterodyne laser can be brought by a mirror 1434 through the middleof the objective 1414, which is typically hollow.

It should be noted that the setup illustrated in FIG. 14 measures thetemperature distribution by mapping the local near-field, which containsmany frequencies in its spectrum. In another version of such amicroscope, one may prefer (in analogy to FIG. 13) to disperse thewavelengths of the near-field response by a spectrometer. The spectrumcan be used not only to determine the local temperature (i.e., Wien'sdisplacement law) in absolute units, but it is also specific to thelocal optical index of the sample.

Experimental Data:

The physical concept of the present invention has been proven throughuse of a heated AFM-object 502 (near-field source) that was approachedby a pyroelectric detector 504 (near-field receiver). The transferredtotal power from the object 502 to the detector 504 was measured as afunction of object-sample distance z. FIG. 15 shows some of the databefore the object touches the surface (verified by the deflection signalfrom the AFM-cantilever). It reveals a very strong and very short-rangedpower flow when the object/sample are within their near-field regionsvalidating the generation of significant near field IR radiation by athermally excited source. In fact, the 1/e decay constant is <10 nm,which promises comparable lateral resolution. For a CCD readout systembased on this mechanism this lateral resolution would translate todensities up to 1.6 Tbit/in² assuming a bit spacing of 20 nm Theestimated power from the tip to the pyroelectric detector is estimatedto be in the μW-range, which is sufficiently strong for manyapplications.

Although specific embodiments of the invention have been disclosed,those having ordinary skill in the art will understand that changes canbe made to the specific embodiments without departing from the spiritand scope of the invention. The scope of the invention is not to berestricted, therefore, to the specific embodiments. Furthermore, it isintended that the appended claims cover any and all such applications,modifications, and embodiments within the scope of the presentinvention.

1. A high resolution material observation system, comprising: an objecthaving at least one spatial dimension sufficient to support productionof near-field infrared emissions; a holder adapted to receive a sampleto be observed, wherein one of the object and the sample operates as anear-field infrared source, and wherein one of the object and the sampleis a near-field infrared receiver, the near-field infrared receiverbeing different than the near-field infrared source, and wherein theholder is further adapted to position the sample so as to place thenear-field infrared receiver in the near-field infrared emissionsproduced by the near-field infrared source; a thermal excitation unit,adapted to be thermally coupled conductively to the near-field infraredsource so as to conduct thermal energy to and thermally excite thenear-field infrared source, thereby generating a temperature differencebetween the object and the sample so as to cause black body radiationwithin the infrared spectrum; and a detector operable to measure atleast one of a far-field response and a near-field response, the atleast one of the far-field response and the near-field response producedby an excitation of the near-field infrared receiver by the near-fieldinfrared emission produced by the near-field infrared source.
 2. Thehigh resolution material observation system according to claim 1,further comprising: a controller communicatively coupled to the objectand the sample, the controller for positioning the object relative tothe sample.
 3. The high resolution material observation system accordingto claim 1, wherein the detector is operable to measure a near-fieldresponse, and wherein the detector is a near-field microscope whichmeasures the near-field infrared emission.
 4. The high resolutionmaterial observation system according to claim 1, wherein: the objectand the thermal excitation unit comprise a resistive heater, wherein theresistive heater has a length dimension and a width dimension, thelength dimension being substantially equal to one half of a wavelengthof the near-field infrared emission and the width dimension being muchless than the wavelength of the near-field infrared emission, the lengthdimension being perpendicular to the width dimension.
 5. The highresolution material observation system according to claim 4, wherein theresistive heater further comprises a first plate and a second plate,each of the first plate and the second plate having a respective edgethat is perpendicular to the length dimension and larger than the widthdimension.
 6. A method for high-resolution observation of material, themethod comprising: thermally exciting, with a thermal excitation unit, anear-field infrared source, the near-field infrared source comprisingone of an object having at least one spatial dimension sufficient tosupport production of near-field infrared emissions and a sample, thethermal excitation unit being thermally coupled conductively to thenear-field infrared source so as to conduct thermal energy to andthermally excite the near-field infrared source, thereby generating atemperature difference between the object and the sample so as to causeblack body radiation within the infrared spectrum; positioning thesample so as to place a near-field receiver in the near-field infraredemissions, wherein the near-field receiver is one of the object and thesample, and wherein the near-field receiver is different than thenear-field infrared source; and measuring at least one of a far-fieldresponse and a near-field response, the at least one of the far-fieldresponse and the near-field response produced by an excitation of thenear-field receiver by the near-field infrared emission produced by thenear-field infrared source.
 7. The method according to claim 6, whereinthe positioning is performed by a controller communicatively coupled tothe object and the sample, the controller for positioning the objectrelative to the sample.
 8. The method according to claim 6, wherein themeasuring comprises measuring a near-field response, and wherein anear-field microscope is used to measure the near-field infraredemission.
 9. The method according to claim 6, wherein: the object andthe thermal excitation unit comprise a resistive heater, wherein theresistive heater has a length dimension and a width dimension, thelength dimension being substantially equal to one half of a wavelengthof the near-field infrared emission and the width dimension being muchless than the wavelength of the near-field infrared emission, the lengthdimension being perpendicular to the width dimension.
 10. The methodaccording to claim 9, wherein the resistive heater further comprises afirst plate and a second plate, each of the first plate and the secondplate having a respective edge that is perpendicular to the lengthdimension and larger than the width dimension.
 11. A computer programproduct for high-resolution observation of material, the computerprogram product comprising: a storage medium readable by a processingcircuit and storing instructions for execution by the processing circuitfor performing a method comprising: thermally exciting, with a thermalexcitation unit, a near-field infrared source, the near-field infraredsource comprising one of an object having at least one spatial dimensionsufficient to support production of near-field infrared emissions and asample, the thermal excitation unit being thermally coupled conductivelyto the near-field infrared source so as to conduct thermal energy to andthermally excite the near-field infrared source, thereby generating atemperature difference between the object and the sample so as to causeblack body radiation within the infrared spectrum; positioning thesample so as to place a near-field receiver in the near-field infraredemissions, wherein the near-field receiver is one of the object and thesample, and wherein the near-field receiver is different than thenear-field infrared source; and measuring at least one of a far-fieldresponse and a near-field response, the at least one of the far-fieldresponse and the near-field response produced by an excitation of thenear-field receiver by the near-field infrared emission produced by thenear-field infrared source.
 12. The computer program product accordingto claim 11, wherein the positioning is performed by a controllercommunicatively coupled to the object and the sample, the controller forpositioning the object relative to the sample.
 13. The computer programproduct according to claim 11, wherein the measuring comprises measuringa near-field response, and wherein a near-field microscope is used tomeasure the near-field infrared emission.
 14. The computer programproduct according to claim 11, wherein: the object and the thermalexcitation unit comprise a resistive heater, wherein the resistiveheater has a length dimension and a width dimension, the lengthdimension being substantially equal to one half of a wavelength of thenear-field infrared emission and the width dimension being much lessthan the wavelength of the near-field infrared emission, the lengthdimension being perpendicular to the width dimension.
 15. The computerprogram product according to claim 14, wherein the resistive heaterfurther comprises a first plate and a second plate, each of the firstplate and the second plate having a respective edge that isperpendicular to the length dimension and larger than the widthdimension.